The present invention relates to a centerless grinding apparatus of the through-feed type in which a work, such as a fluid-operated piston for use in disc brakes, is fed by a regulating feed wheel in a direction of the axis of the work, and an outer peripheral surface of the work is ground by a grinding wheel.
Generally, as shown in FIGS. 1 to 3, a centerless grinding apparatus of the through-feed type comprises a grinding wheel 1 and a regulating feed wheel 2 disposed in opposed position to the grinding wheel 1. In such a conventional centerless grinding apparatus, the regulating feed wheel 2 is inclined with respect to the grinding wheel 1 in a direction of feed so as to feed a work W in the direction of the axis of the work through the rotation of the regulating feed wheel 2. A blade 5 for supporting the work W is provided between the grinding wheel 1 and the regulating feed wheel 2 at a lower position. Further, in order to guide the feed of the work W, guide plates 3A, 4A each in the form of a flat plate are arranged on the work incoming side of the opposed grinding and regulating feed wheels 1 and 2 in parallel relation to each other. Similarly, guide plates 3B, 4B each in the form of a flat plate are arranged on the work outgoing side in parallel relation to each other.
As shown in FIG. 1, the grinding wheel 1 is set to protruded from a guide surface 3a of each of the guide plates 3A, 3B by a grinding width having a dimension A, and the regulating feed wheel 2 is set to protrude from a guide surface 4a of each of the guide plates 4A, 4B by a feed width having a dimension B. Normally, the grinding width A is set to 0.2 to 0.4 mm, and the feed width B is set to 0.01 to 0.03 mm.
When the work W is guided by the guide plates 3A, 4A and is introduced between the grinding wheel 1 and the regulating feed wheel 2, the work W is rotated and fed in the direction if its axis by the regulating feed wheel 2 protruding by the feed width B. At the same time, the work is ground by the grinding wheel 1, and then the work is guided by the guide plates 3B, 4B and delivered.
With such a conventional apparatus, where it is intended to grind many kinds of works W1, W2 having different diameters, the following problems may be raised.
Here, it is assumed that the spacing between the grinding wheel 1 and the regulating feed wheel 2 as well as the grinding width A1 and the feed width B1 have been set in accordance with the work W1 having greater diameter, as shown in FIG. 2.
In this condition, when the apparatus is to be operated for grinding the work W2 having a smaller diameter, the positional relationship of the parts of the apparatus have to be adjusted because of the differences in diameter between the smaller diameter work W2 and the greater diameter work W1.
In this adjustment, if the guide plates 4A, 4B and the regulating feed wheel 2 are merely moved horizontally toward the grinding wheel 1 with the height of the blade 5 unchanged, a point of contact of the work W2 with the regulating feed wheel 2 must be moved to a lower position by an amount corresponding to the difference in diameter between the smaller diameter work W2 and the greater diameter work W1.
As shown in FIG. 3, at this lowered point of contact, the width B2 of protrusion (feed width) of the regulating feed wheel 2 from the guide surface 4a of the guide plate 4A is narrower than the width B1, so that the regulating feed wheel 2 cannot sufficiently apply the force to the work W2. Accordingly, the contact of the work W2 with the grinding wheel 1 becomes uneven, so that a grinding deficiency, that is, failure to obtain roundness of the ground surface, occurs.
Therefore, every time the work W is changed, the adjustment of the positional relationship of the parts of the apparatus, including the adjustment of the height of the blade 5, must be entirely made so as to set the point of contact of the work W with the regulating feed wheel 2 to the optimum position. However, the feed width B is quite small, and conventionally, this adjustment depends on the sense of sight and sensation of the operator and ,therefore, much skill would be required. If an unskillful person makes this adjustment, variations in the adjustment occur, which would raise the above-mentioned grinding deficiency.